I have done something similar. Your property looks to be about 100' +/- across. At that width, you shouldn't need too much height. I'd guess around 50' should do it. You would probably want more altitude when you get back by the trees. It really is a preference thing. Try a few runs and see what the results are. Raise lower the altitude until you get what you want.
Regarding camera orientation...
When using the DJI Go app with the "Waypoints" feature, it will remember where the camera is pointed at each waypoint. To set up a waypoint "mission" you must manually fly to each point and set it. Once done, you can save the mission and replay it.
Fly to waypoint "A" and point he camera where you want. Record the waypoint. Repeat for each waypoint. The position, altitude and orientation of the P3 will be recorded for each waypoint. I do not believe the gimbal pitch is recorded. IMO, best way is to find some gimbal pitch setting that will work for the entire run... much smoother video that way.
When you replay the mission, you are given a choice regarding the camera. You can set it to "free" and control the camera. You can set it to point in the direction of flight. The third choice allows you to have the camera point where is way when the waypoint was recorded.
Altitude, orientation and position are all interpolated between waypoints. Take this into account. If waypoint A is 50' high and waypoint B is 100' high, halfway between the two points you will end up at about 75'. Think about that when planing a route over a structure or those trees.